Substrate processing used in the manufacture of semiconductor devices and other electronics is a carefully controlled process that often involves close monitoring and post-processing inspection and analysis in order to optimize fabrication processes and improve yield. Advancements in fabrication processes and fab level automated material handling systems (AMHS) have led to a high degree of automation that has improved efficiency in many aspects of substrate processes. Material handling systems often include systems that automatically transport lots of substrates among different tools in specialized carriers, commonly front opening unified pods (FOUP), and robotic handlers may be used at the tools to load individual substrates from the carriers onto a stage for processing or post-processing review.
Occasionally, undesired particles and other contaminants can have adverse effects on fabrication, and post processing review, e.g., inspection, metrology, or other analysis, is often used to gather information regarding processing conditions and other useful information. To combat this and gather more useful information, special substrate-like sensor devices, sometimes known as “sensor wafers” when used in the context of semiconductor wafer processing, are often used along with the ordinary production substrates (e.g., production wafers fabricated into operational electronic devices) in order to gather additional information regarding processing conditions. Typically, these substrate devices are designed to have dimensions and other physical parameters similar to the production substrates of interest in order to closely approximate the effects of processing conditions on production substrates, but usually these substrate devices also include additional specialized electronics for extracting additional data. These sensor wafers may be placed in a FOUP along with other production substrates and placed in a production chamber in a manner similar to other substrates. Data is typically subsequently extracted after the relevant processing stage to obtain additional useful information regarding processing conditions.
In many situations related to substrate processing and post-processing inspection, precise positioning and positional information is critical. For example, an inspection tool may have an electron microscope or other electron beam system capable of resolving features at a very small micro- or nano-scale, but conversely have a very narrow field of view that requires the substrate to be precisely positioned relative to the tool in order to locate particular particles or defects on the substrate and gather useful data. Precise information regarding the position of a substrate relative to the tool thus becomes critical for locating a particular small scale defect, particle, or other area of interest on the substrate. In these situations, a time consuming process requiring manual intervention is typically used. This usually involves manually mounting optics, sighting the wafer in (using wafer targets), and manually entering positional offsets to the wafer handlers.